What's going on? Exhale, FRC, BO, CO2, safety.

[cdavis]

Me too. My starting assumption is that Eric is right. But he is also very very precise within a much larger knowledge base than mine, so I often don't understand what he said. Case in point.

 

[baiyoke]

For my part, my point of reference is, as stated before (to keep it simpel) a static emptylung.

EricF made a good point earlier, forget the theory and go test. Most of this stuff is very testable, especially if you have a pool available with 4 meters or more of depth.

Connor

This thread is for me about understanding the theory behind, so that advice is not helping me out... I am quite convinced allready that things work like people say, and that it is at depth-diving it is beneficial. Here I just want to understand what is going on in the body, breaking it down, starting with emptylung as the first factor i.e. emptylung static.

From experience,I'm pretty sure about c02 contributing to DR.

Connor

For sure CO2 contribute to DR (in general). But I can not see how CO2 can rise so quickly on emptylung static apnea, my "research" on deeperblue has not revealed it, and nobody has been able to explain it in any post I have read. On the other hand, more likely scenarios have been mentioned in different threads (see earlier post).

Connor

Thanks for the answer, it makes sense and is in fact exactly what I posted above, see post #5 in this thread.

But what is confusing me is Eric's comment:

Originally Posted by efattah: "Blood CO2 is always lower on an exhale STATIC (not dive) because the ratio of gas:blood is lower."

When there is not as much GAS/air/O2 in the lungs - and the amount of blood is the same - the amount of CO2 made will be smaller during the apnea.
This makes sense to me, except for the detail that early vasoconstriction might keep the CO2 in the lung-heart-brain system, an therefore theoretically it might rise more than the ratio initially indicated I would speculate.

The above is exactly why I can't see CO2 be the primary (or secondary) DR trigger.

Remember Eric is talking about a static at the surface, so I'm not sure DR is a factor. Or maybe it is. Eric?

DR is just as much a factor on the surface - Just works slightly different and stronger at depth / submerged I would say etc.

 

[Kars]

DR is triggered by various things.
Thinking about diving can even trigger a DR.

I think that one reason DR kicks in more easily in reduced volume diving, is a lower heart-rate, blood pressure and blood flow after exhale. Also after exhale diving deep, the artery and heart has room to move, reducing blood flow even more.
I've come to these ideas after testing in a pool in search of understanding why my static is nice, but my dynamic sucks, or to be precise why my muscles don't acid up and I have to surface because of low O2 to the brain.

 

[growingupninja]

DR is triggered by various things.
Thinking about diving can even trigger a DR.

I think that one reason DR kicks in more easily in reduced volume diving, is a lower heart-rate, blood pressure and blood flow after exhale. Also after exhale diving deep, the artery and heart has room to move, reducing blood flow even more.
I've come to these ideas after testing in a pool in search of understanding why my static is nice, but my dynamic sucks, or to be precise why my muscles don't acid up and I have to surface because of low O2 to the brain.

Kars, have you tested your DYN, in water, while wearing a heart rate monitor? Or done some experiments with a medium wet static hold (like maybe 2-3 minutes--nothing extreme but enough for your DR to kick in), followed immediately by some DYN swimming while on the same hold? I would be curious what your numbers are since you report that you can swim DYN without a great deal of lactic build-up, but run the risk of samba/BO from low O2 when doing so. Perhaps your 'work response' (re: Seb's exhale thread) is very strong so if you are doing a static, your DR kicks in nicely but when you begin to swim, work response takes over, supplying your muscles with blood which keeps them from shutting down from lactic acid but which takes blood from your core. Has your body always responded this way on DYN vs static?

 

[Kars]

Yes I did tests like that wearing a HR monitor.

my pb static: 7'
my pb dynamic: 150m
my pb dnf: 111m (2005!)

I found that controlling my blood flow is essential. I got a very good condition, extremely low fat, thin arms and legs, tall figure. In all the blood supply potential to my muscles is high. My heart is very efficient supplying the muscles too. The result is that blood shift occurs late, and appears to be only a minor slowing down of the blood flow to my muscles. Hence my muscles deplete my lungs and blood very efficiently from O2.

I did dnf dives of just 50m to compare.
Both dives full lungs, diving with different goals in mind. First normal dnf dive, relax, and go at a speed I would do for a pb. 1m/s. Contraction at 40m (normal). No lactic acid felt.
Second dive, with intention to keep blood flow low. Gentle push, less arm power, thinking my hr and blood flow down, going much smoother through the water.
Felt hardly any contraction after 50, felt much less urge to breath, felt a really nice lactic acid burn (that made me smile!), and much clearer mind!

Watching my graphs of my HR falling in dnf apnea, I only see that in sub full lungs the HR is starting off lower, but within about 25 seconds both full and empty lungs reach the same bottom numbers (45). Then arching down to (35) until the first contraction. These numbers can be deceiving though, because the hart can pump different volumes per beat. So I recognise that blood flow is the number to look for. Especially low blood flow.
Talking to a static king in progress, he told me his muscles get too little blood flow, resulting in him needing to surface. From this range of people I think part of advanced freediving is regulating blood flow so as muscle failure and samba meet just 1m after your exit. Finding this balance is a challenge.


ps. The funny thing is that in deep diving, when I'm relaxed, the lactic acid appears to manifest easier there than doing dynamics. This leads me to suspect that the pressure helps to reduce blood flow.
pps. In testing the bloodflow thesis I unexpectedly reached near my pb, doing 106 m. My second longest to date.

 

[Siku]

When there is not as much GAS/air/O2 in the lungs - and the amount of blood is the same - the amount of CO2 made will be smaller during the apnea.

Why?

At the risk of repeating myself, I've explained three times in this thread why the exact reverse is true: lower lung volume = higher CO2.

I'm quite prepared to be wrong, but can someone please explain why?

(Remember this claim is being made excluding the effects of DR and vasoconstriction, which obviously will lower CO2 in core, as outlined by myself and Connor and others in this thread.).

 

[baiyoke]

Why?

At the risk of repeating myself, I've explained three times in this thread why the exact reverse is true: lower lung volume = higher CO2.

I'm quite prepared to be wrong, but can someone please explain why?

(Remember this claim is being made excluding the effects of DR and vasoconstriction, which obviously will lower CO2 in core, as outlined by myself and Connor and others in this thread.).

As I understand it, because there is not enough O2 in the system to drive up CO2 measures to the same heights as on full-lung. Even if what you describe is true.

 

[baiyoke]

Btw I think this is an important information from Eric, as mentioned before, when looking isolated at CO2 on full vs. empty lungs:

Blood CO2 is always lower on an exhale STATIC (not dive) because the ratio of gas:blood is lower. Since hemoglobin can both attach O2 and CO2 then the blood has both O2 storage and CO2 buffering, whereas the lungs have strongly unequal O2 storage and CO2 storage.

This part: whereas the lungs have strongly unequal O2 storage and CO2 storage.

Eric, now things are getting more complicated What do you mean by this "hemoglobin can both attach O2 and CO2 then the blood has both O2 storage and CO2 buffering, whereas the lungs have strongly unequal O2 storage and CO2 storage." How are the lungs storage capabilities described? I would suspect "more oxygen, less CO2 buffer"-capabilities...? Right? That is why CO2 level increase more on full lungs right? Anf if someone had say 40 litres lungs, that person would overwhelmed by too high CO2 levels long before oxygen would run out, right?

Allthough Eric has not commented on this.

But overall, as I stated before, I don't see CO2 being the most important part of the DR triggering on emptylung statics. This however would highlight why BO is more likely to happen on a STATIC emptylung apnea.

Eric?

 

[growingupninja]

Why?

At the risk of repeating myself, I've explained three times in this thread why the exact reverse is true: lower lung volume = higher CO2.

I'm quite prepared to be wrong, but can someone please explain why?

(Remember this claim is being made excluding the effects of DR and vasoconstriction, which obviously will lower CO2 in core, as outlined by myself and Connor and others in this thread.).

This kind of detailed physiology is a little outside my pay grade but I think lower lung volume = less CO2 because stronger dive response means metabolism slows down faster and CO2 is a natural metabolic by product, so less is being produced, and because the hemoglobin in your body is independent of lung volume, and so there is less gas in the lung to buffer it but the same amount of CO2, hence the ratio changes.

 

[growingupninja]

Yes I did tests like that wearing a HR monitor.

my pb static: 7'
my pb dynamic: 150m
my pb dnf: 111m (2005!)

I found that controlling my blood flow is essential. I got a very good condition, extremely low fat, thin arms and legs, tall figure. In all the blood supply potential to my muscles is high. My heart is very efficient supplying the muscles too. The result is that blood shift occurs late, and appears to be only a minor slowing down of the blood flow to my muscles. Hence my muscles deplete my lungs and blood very efficiently from O2.

I did dnf dives of just 50m to compare.
Both dives full lungs, diving with different goals in mind. First normal dnf dive, relax, and go at a speed I would do for a pb. 1m/s. Contraction at 40m (normal). No lactic acid felt.
Second dive, with intention to keep blood flow low. Gentle push, less arm power, thinking my hr and blood flow down, going much smoother through the water.
Felt hardly any contraction after 50, felt much less urge to breath, felt a really nice lactic acid burn (that made me smile!), and much clearer mind!

Watching my graphs of my HR falling in dnf apnea, I only see that in sub full lungs the HR is starting off lower, but within about 25 seconds both full and empty lungs reach the same bottom numbers (45). Then arching down to (35) until the first contraction. These numbers can be deceiving though, because the hart can pump different volumes per beat. So I recognise that blood flow is the number to look for. Especially low blood flow.
Talking to a static king in progress, he told me his muscles get too little blood flow, resulting in him needing to surface. From this range of people I think part of advanced freediving is regulating blood flow so as muscle failure and samba meet just 1m after your exit. Finding this balance is a challenge.


ps. The funny thing is that in deep diving, when I'm relaxed, the lactic acid appears to manifest easier there than doing dynamics. This leads me to suspect that the pressure helps to reduce blood flow.
pps. In testing the bloodflow thesis I unexpectedly reached near my pb, doing 106 m. My second longest to date.

Thanks, Kars. 'regulating blood flow so as muscle failure and samba meet just 1m after exit' makes sense for competition and situations where you have active safety. For pool dynamics maybe I should play with sprints or near sprints for a max attempt. I had assumed the best thing would be for me to start really slow and establish a strong DR, but vasoconstriction is so strong that I feel like my muscles are failing before I am especially hypoxic on DYN, and this is supported by tests I've done dry on a pulse O2 meter. From experience, DR can be delayed if I am exerting myself, and I had been approaching DYN much like I would a deep spearing dive--very, very slow relaxed start to maximize DR, which makes for a safer dive. However, my deepest spearing dives don't even cover 100M in total distance, so I am happy to trade lowered O2 consumption for some lactic burn, and since on a deep spearing dive I am typically only kicking 50M to 75M muscle failure is a non-issue.

Yes, I think depth/pressure definitely is a significant trigger for vasoconstriction. If I do a spearing dive to 15M in winter water where I am kneeling on the bottom for a couple minutes, I will surface with no O2 depletion, but the lactic burn in my legs may be comparable to swimming 65M DYN from vasoconstriction, even though my distance traveled on the spearing dive is closer to 25M.

BTW, this is the pulse O2 meter I use. It has a little cardio graph which is useful since you can actually see vasoconstriction happening. I need to do better tests, but yes I agree, the heart can pump different volumes to the peripheries and it's important to remember that. Some tests, even with same amount of bradycardia (forties is my first plateau) I seem to see a difference in vasoconstriction which is primarily dependent on water temp.

'OxyWatch 300CA Professional Series Finger Pulse Oximeter'

 

[Siku]

Thanks for the answers everyone. So far we’ve got:




CO2 is higher diving empty/FRC because:

• Lower lung volume slows rate of offloading from blood to lungs

CO2 is lower diving empty/FRC because:

• DR - Muscles click into anaerobic mode more quickly, reducing CO2 production
• DR - Metabolism lowers more quickly, reducing CO2 production
• DR - Vasoconstriction reduces blood flow bringing CO2 back to the core

• Not enough O2 in the system to drive up CO2 (baiyoke)
• Hemoglobin in your body is independent of lung volume, and so there is less gas in the lung to buffer it but the same amount of CO2, hence the ratio changes (growingupninja)

So, baiyoke, CO2 production requires O2? I wasn’t aware of that, except in so far as low O2 would correspond to anaerobic mode. Is there less O2? Eric seemed to suggest so when he said it is easier to hold to BO. But according to Seb’s theory empty lung preserves O2 stores.

growingupninja, I can see that the ratio of blood CO2 to lung CO2 changes, but doesn’t this work the other way round: Less in lungs = more in blood where the receptors are?

 

[baiyoke]

So, baiyoke, CO2 production requires O2? I wasn’t aware of that, except in so far as low O2 would correspond to anaerobic mode.

I don't recall having said that??? I dont know if other processes (anaerobic) can produce the same amount of CO2. But the brain requires O2, otherwise you blackout. If indeed the lungs O2 capacity is far greater than it's CO2 buffering capabilities (wich it looks like, but wich is still not established as a fact here), then a person with, say, 500 L lungs would be able to drive up CO2 to skyhigh measures, and still have plenty of oxygen for the brain.

Is there less O2? Eric seemed to suggest so when he said it is easier to hold to BO. But according to Seb’s theory empty lung preserves O2 stores.

As far as I understand it, both are right. Wich is why emptylung works. Less O2 in beginning (obviously), but a more economic use of it.

What I can't understand is, why Seb and other emptylung divers call it safer. I can see there's a more economic use of oxygen, but since full-lung divers also get into divemode eventually, I can only see exhale as less safe, because of lower CO2 alarm. But I sense that there are perhaps other things at work here... Perhaps something like a stronger DR makes the road to BO less steep and more gradual... But that again does only make sense, if we had BO-detection, wich we does not seem to have really.

 

[growingupninja]

What I can't understand is, why Seb and other emptylung divers call it safer. I can see there's a more economic use of oxygen, but since full-lung divers also get into divemode eventually, I can only see exhale as less safe, because of lower CO2 alarm. But I sense that there are perhaps other things at work here... Perhaps something like a stronger DR makes the road to BO less steep and more gradual... But that again does only make sense, if we had BO-detection, wich we does not seem to have really.

Seb could explain it better himself, but empty lung diving seems to have a very strong effect on 'work response'/'ascent tachycardia' in many divers, with Seb--based on his theories and HR dive profiles he has posted on some other threads--being a prime example. On some sled dives which were deepish but certainly not extreme, he showed very limited dive response and strong ascent tachycardia on a full lung, but his exhale dives showed a strong, nearly instant dive response that was stable throughout the entire drop, and then continued for many seconds AFTER he surfaced and began breathing. He theorized that ascent tachycardia (rise in HR during the ascent phase of a dive) could increase the risk of BO, and ancedotal evidence seems to support this...

Empty lung diving doesn't seem to affect everyone the same however. From much more limited tests that I have done on myself, I typically get the same dive response whether empty or full. Empty just kicks in a little faster.. like 30 secs vs 60 secs, and my HR does stay lower for longer after I begin to breathe. But I don't seem to experience significant ascent tachycardia or work response on either type of diving after DR kicks in. For extremely deep dives or serial deepish dives, the narcosis and reduced DCS factor of empty lung diving could possibly make it safer, and less CO2 would result in a clearer head--although if you dive/train full lung, you can certainly condition for CO2 tolerance.

Basically, diving with the strongest possible DR is the safest way to dive. For some people, empty lung/FRC seems to motivate a much stronger DR than full lung, so for those people it could be safer.

 

[trux]

I did not have time until now to have a look at this thread, but see there are too many wrong assumptions and claims made there, so for the future visitors I think it may be worth of clearing up at least some of them.

CO2 is lower during exhale because:
1) You start with less O2, hence you produce less CO2 (CO2 is a metabolic product of oxygenation)
2) The DR is stronger, the metabolism lower, and muscles work in anaerobic mode earlier (hence not producing CO2)
3) As Eric wrote, the ratio of the two stores lungs and blood is much lower on exhale, and because the buffer capacity of lungs is very limited, it has a great impact. Very roughly on inhale the lungs contain around half of the O2 available, while the blood contains the rest. In the same time, the lungs even at a very progressed apnea contain just a few % of the overall CO2 that is in the body. 70-80% of CO2 is in the form of bicarbonate in the red blood cells, 5-10% is dissolved in the plasma, and 5-10% is bound to hemoglobin as carbamino compounds. So while the full lungs contain around half of the O2, they can only buffer a tiny fraction of the total CO2. It means that when you decrease the lung/blood ratio by exhaling, the buffering capacity does not change much, while the production is limited (due to lower available O2 and lower metabolism). Hence the CO2 level will be lower.

Strong DR is not depending on the CO2. According to studies, CO2 does not seem to be a major DR contributor.

Empty lungs has its own risks (low CO2 as mentioned by Eric and Seb, and also higher risk of inhaling water on BO), but basically, if we speak about dynamic or depth diving with a strong DR, the added safety factor comes from that aspect that muscle failure or strong discomfort from lactic acid usually terminates the dive before you are deep in dangerous hypoxia. But this is strongly individual, and depending on other factors, so cannot be taken as a guarantee of a safe dive!

 

[cdavis]

Good explanation of some of the physiology, Trux. Thanks

The role of C02 in DR is not understood all that well. I would not argue with the idea that it is not a major contributor, but it certainly seems to have some effect, especially in early onset of DR, a major goal of exhale divers. I get longer, more comfortable dives if I take down slightly more C02 than normal and no other difference. On the flip side, slight hyperventilation shortens my exhale dives. Sure seems like the extra C02 is starting the DR process quicker.

 

[Siku]

Trux

Thanks for confirming that O2 is required to produce CO2. I wasn't aware of that although looking at the chemistry I suppose it should have been reasonably obvious!

And for clarifyning Eric's point that the buffering capacity, as you call it, or offloading of CO2, as I said, is only a small % of CO storage, and therefore any change in lung volume is a minimal facotor, IIUC.

A very informative thread, thanks to all

Sooooo, why are empty/FRC breath holds (e.g. dry) SO much harder than full lung?

 

[trux]

Sooooo, why are empty/FRC breath holds (e.g. dry) SO much harder than full lung?

Because the comfort phase is much shorter, and the DR kicks in quicker. At the beginning (comfort phase), the CO2 rises approximately in the same rate as on full lungs - there is high consumption, high metabolism, and about the same availability of free CO2 buffers, so the situation does not differ much from full lungs. Perhaps even a bit faster than on inhale, because lungs are used for buffering O2 especially at the beginning, when the gradient of PaCO2/PACO2 is big enough; later in the breath-hold, the diffusion of CO2 to lungs is very limited (both on inhale and exhale). The rising of CO2 on FRC only slows down when the DR kicks in, which happens relatively quickly on FRC.

The level of CO2 at the end will be lower on exhale than on inhlae, but at the beginning it won't differ that much. It means you can reach certain level of CO2 driven discomfort at the beginning, which is then amplified by other factors (empty lungs feeling, relatively lower PO2, mental, ...). And in fact divers who practise FRC diving do not really feel it is SO much harder than full lungs.

 

[cdavis]

"And in fact divers who practise FRC diving do not really feel it is SO much harder than full lungs."

Exactly!

There is a considerable difference in discomfort between an empty lung static, dry or wet, and doing the same thing about 1/2 lung. Dead empty the comfort phase is very short and co2 level gets pretty high in the core before the DR can kick in fully, at least for me. Also for me, getting FRC diving to work right is a balancing act between lung size, co2 buildup, and getting the DR to set in fast enough. Get it right and you end up with a long comfortable safe dive. Takes practice.

Connor

 

[Gletwyn Rubidge]

I have been full doing exhale dives to between 5 and 8 m. I do not push it to 60 sec for safety. Interestingly on exhale dives I hear my heartbeat loud and clear - after about 30 sec at 7-8 m my pulse drops from mid 50 s to between 28 and 30 bpm - timed by audible heartbeats against watch. I try to hear my heartbeat on full lungs and there is no sound. Can anyone offer an explanation for the difference?

 

[growingupninja]

Blood pressure could have a lot to do with it. If you are experiencing that kind of bradycardia, I am sure your blood pressure would be very high. On a full lung you might not experience that combination of bradycardia/high bp.

If you ever do statics wearing a blood pressure cuff you will see it rise as contractions/struggle phase starts.